1. Field of the Invention
The present invention relates to a bonded laminate structure, a hose containing the bonded laminate structure, and methods for producing the same.
2. Description of the Art
To comply with recent stricter regulations against automotive evaporative emissions, various types of less permeable fuel hoses have been under consideration. Less permeable resins such as polybutylene naphthalate (PBN) and polybutylene terephthalate (PBT) are typically employed as materials for such hoses.
However, a hose having a low-permeability resin layer of PBN or PBT alone is unacceptable because of its high rigidity. Therefore, it is a common practice to provide a laminate structure comprising a low-permeability resin layer having a reduced thickness and a thermoplastic resin layer such as of a polyamide. However, since PBN and PBT do not adhere well to the thermoplastic resin (e.g., polyamide), the provision of an adhesive layer between the low-permeability resin layer of PBN (or PBT) and the thermoplastic resin layer is required. This complicates the structure of the hose, and increases the costs due to the use of a costly adhesive material. In addition, an extrusion process employing the adhesive material requires a higher temperature setting to provide enhanced adhesion. This higher temperature may result in instability of the properties of the hose, because PBN and PBT are susceptible to molecular degradation when being subjected to a high temperature.
In view of the foregoing, it is an object of the present invention to provide a bonded laminate structure which is obtainable by bonding a PBN layer (or a PBT layer) to a thermoplastic resin layer without the use of an adhesive material, a hose having such a bonded laminate structure, and methods for producing the same.
In accordance with a first aspect of the present invention to achieve the aforesaid object, there is provided a bonded laminate structure which comprises: a first layer comprising at least one of polybutylene naphthalate (PBN) and polybutylene terephthalate (PBT) as an essential component and having a surface subjected to an electric discharge treatment such as a plasma treatment; and a second layer comprising an amine-rich resin as an essential component and bonded to the surface of the first layer.
In accordance with a second aspect of the present invention, there is provided a hose which comprises a bonded laminate structure according to the first inventive aspect, wherein the first layer thereof is provided radially inwardly of the second layer thereof.
In accordance with a third aspect of the present invention, there is provided a method for producing a bonded laminate structure according to the first inventive aspect, which comprises the steps of: subjecting a surface of a first layer comprising at least one of polybutylene naphthalate and polybutylene terephthalate as an essential component to an electric discharge treatment such as a plasma treatment to cause the surface of the first layer to have an oxygen-to-carbon atomic ratio (O/C) of not smaller than 0.35; and bonding a second layer comprising an amine-rich resin as an essential component to the surface of the first layer.
In accordance with a fourth aspect of the present invention, there is provided a method for producing a hose according to the second inventive aspect, which comprises the steps of: subjecting an outer surface of a first layer comprising at least one of polybutylene naphthalate and polybutylene terephthalate as an essential component to an electric discharge treatment such as a plasma treatment to cause the outer surface of the first layer to have an oxygen-to-carbon atomic ratio (O/C) of not smaller than 0.35; and bonding a second layer comprising an amine-rich resin as an essential component to the outer surface of the first layer, whereby the first layer is provided radially inwardly of the second layer.
The inventors of the present invention have conducted intensive studies to provide a bonded laminate structure which is obtainable by bonding a PBN layer (or a PBT layer) to a thermoplastic resin layer without the use of an adhesive material. As a result, the inventors have found that the intended object is attainable by subjecting a surface of a first layer comprising at least one of polybutylene naphthalate (PBN) and polybutylene terephthalate (PBT) as an essential component to an electric discharge treatment such as a plasma treatment, and bonding a second layer comprising an amine-rich resin as an essential component to the surface of the first layer to provide a bonded laminate structure comprising the first layer and the second layer. Thus, the present invention has been achieved. By activating the surface of the first layer to be bonded to the second layer through the electric discharge treatment (e.g., plasma treatment), hydrogen atoms are removed from the molecular skeleton of PBN or PBT, so that carbon radicals are generated in the surface. The surface of the first layer is at least partly strengthened by a cross-linking reaction caused by some of the carbon radicals. The other carbon radicals in the surface of the first layer bond to oxygen in air, thereby forming functional groups such as hydroxyl groups, carboxyl groups, aldehyde groups, and ketone groups. On the other hand, the second layer comprising the amine-rich resin has a higher amino group content than an ordinary or conventional resin, because the amine-rich resin is typically obtained by mixing a compound having amino groups with a thermoplastic resin such as a polyamide or by causing the compound having amino groups to react with the thermoplastic resin. Therefore, the amino groups in the second layer have a remarkable affinity for the functional groups in the surface of the first layer. This supposedly provides adhesion between the first layer and the second layer.
In the present invention, the amine-rich resin is defined as having an amino group content of not lower than about 4.5xc3x9710xe2x88x925 g equivalents/g.